When I get a good snap, it feels like it phantom jumps out of my hand. I grip down at the hit, and then poof it's gone and going the speed of sound down the fairway, it's really odd... Is this indicative of improper timing?

I use a reachback method now where I actually bring the disc out to the right of my body during the reachback and then bring it in at my chest during the pullthrough as opposed to reaching straight back or starting bent elbow (both of which I tried for a long time). This has really helped me get consistent with my timing. Now I know all my power is coming from elbow extension because even my throws that come through to close and hit my chest get out a ways.
I was playing today and I was emphazing delaying the elbow chop where I bring the disc in to my chest and I started feeling the wrist movement in my throws. I was actually able to really pinpoint when my wrist stopped wagging back and started moving forward but even trying to grip hard at that point didn't get me much extra distance. I'm not sure where to go from here because I'm still only driving about 320'. A couple pretty good players have told me that I have good form I should just speed everyting up. I'm am pretty slow paced on the pad without a big runup, but everytime I try to add steps or go through the motions faster I get less or the same distance because it screws up my timing. But I still think I should be able to throw 350' at the speed I'm going.

I don't quite understand what you're describing in terms of a reachback... you dont need to necessarily speed everything up, just focus 80% your power slightly after the disc passes your chest. Have your hips lead your shoulders too, that really helps build that strong snap without feeling like you're speeding things up, when in actuality you are.